(1) Field of the Invention
The present invention relates to a method and apparatus for processing a radiation image formed by the photographing using radiations such as X-rays and .gamma.-rays.
(2) Description of the Related Art
If a radiation image is digitized and is connected through a network, processing, transmission, storage and retrieval of the image become possible, and the diagnosis by a doctor is facilitated. However, a radiation image having a high diagnosis performance is required. Furthermore, in order to increase the performance of the diagnosis by the doctor, the radiation image should be subjected to an appropriate image processing, and among such image processings, a gradation processing is simple and a high effect is attained by this treatment. The conventional image processing by the gradation processing will now be described.
When the radiation image is subjected to the gradation processing, the gradation processing conditions are determined from statistical characteristics of data of the entire image (maximum and minimum values of data, histograms and the like), and the gradation processing of the entire image is carried out under these conditions (see Japanese Examined Patent Publication No. 63-31641 and Japanese Unexamined Patent Publication No. 1-33818).
In the case where the radiation image is a chest image, only a part of the pulmonary region is necessary in the image. If the gradation processing conditions are determined based on the statistical characteristics of data including those of unnecessary portions, an optimum gradation processing cannot be attained and optimum data for the necessary portion cannot be obtained. If the irradiation area is limited to the pulmonary region, there appears a portion having data equivalent almost to zero, and if the gradation processing conditions are determined from the statistical characteristics of data including data of this portion, optimum gradation processing results cannot be obtained.